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I Case Closure Report Former Tosco(Unocal) SS No 5421, Stockton, California July 8, 1998 • Well Survey A water supply well survey was conducted in June 1996 by Pacific by reviewing available files at the California Department of Water Resources (DWR) The well survey identified active and inactive water supply wells within a 1/4-mile radius of the subject site The identification of monitoring and extraction wells associated with groundwater remediation activities was not included in the well survey Twenty documented wells were identified within the area examined The closest well appears to be located approximately 500 feet west and up-gradient of the site The closest well down-gradient of the site is located outside of the 1/4-mile radius and is listed as municipal well (Inglewood Station) This well is 317 feet deep and is most likely completed in a much deeper water bearing zone A Site Location and Well Survey Map, and a completed Table listing all identified wells is presented in Appendix C Summary Soil Contamination Delineation Based on the analytical results of all of the soil samples collected and evaluated to date, the vertical and lateral extent of residual petroleum hydrocarbon impacted soil is well defined and very limited in extent The analytical results of all of the soil samples collected from beneath two generations (1989 and 1998) of product piping, dispensers and USTs, indicate a very limited residual petroleum hydrocarbons remaining in the soil beneath the site The removal of the first generation of USTs and piping occurred in 1989 Soil was over-excavated in the area of the islands and UST pit Residual hydrocarbons are limited to the area north of the western dispenser island and the southern limits of the over-excavated UST pit Residual TPHg concentration are documented at 16 ppm and benzene of 0 58 ppm at 13 feet bgs Residual hydrocarbons remaining from the removal of the second generation of USTs in 1998, are also very limited and are documented in the area of the former UST pit The pit was over-excavated to the mechanical limits of the on-site equipment, 26 feet bgs, where a soil sample was reported to contain 24 ppm TPHg and 0 77 ppm benzene The soil samples collected from beneath the dispenser islands were reported a range form non detect to 19 ppm for TPHg and non detected to 0 029 ppm for benzene In addition to the removal of the fuel dispensing facilities at the site, a septic tank, drain line, leach field and seepage pit were removed in October 1992 The septic tank and leach field located in the southwest and along the western property line, was over excavated vertically and laterally Impacted soil was removed and verification samples collected Analytical results were reported as non detected for all samples except in two . locations which contained 13 ppm TPHd and 84 ppm TOG 140162 03 12